If you want to take a day trip from Oslo and immerse yourself in art, history and nature, I recommend taking a trip to Høvik Verk. It is located in Bærum, easily reachable by train or bus from Oslo. A little bit of walking is required to take in all the sights, but that is also part of the attraction.
I recommend starting at Høvikodden, where the art museum Henie Onstad Kunstsenter (HOK) is located. It houses a variety of art exhibitions. A new exhibition on documentary photography just opened, and the also house a permanent exhibit by Yahoo Kusama. They also have a restaurant. Take bus 160 to get here, to the stop Høvikodden (5 mins walking), or the train to Blommenholm (15 mins walking).
Afterwards, visit the sculptures outside and then go for a walk along the sea. You will soon come to Veritasparken, which is an old industrial area turned modern offices, surrounded by a beautiful public park. Some of the old buildings from Høvik Verk glass works have been incorporated into the modern offices of Det Norske Veritas (DNV).
If you keep walking, there is an accessible path along the sea. Enjoy beautiful views, small beaches and a variety of smaller paths. You can turn around whenever you feel like it, or keep walking past Sarbuvollen (you have to go through a residential area) to Stand Restaurant, which serves very nice food in a beautiful location. Turn around whenever you feel like going home.